1. Field of the Invention
The present invention relates to a production method of a light scattering film, a light scattering film, a polarizing plate, an image display device, and a transmissive/semi-transmissive liquid crystal display device.
2. Description of Related Art
In recent years, liquid crystal display devices (LCD) have been used widely because they are thin, are light weight, and consume little power. Liquid crystal display devices each includes a liquid crystal cell and a polarizing plate. The polarizing plate is usually formed of a protective film and a polarizing film and is available by staining a polarizing film made of a polyvinyl alcohol film with iodine, stretching the resulting film, and then stacking a protective film on both sides thereof. In a transmissive liquid-crystal display device, the polarizing plate may be attached onto both sides of a liquid crystal cell and one or more optical compensation sheets may be disposed further. In a reflective liquid crystal display device, it is the common practice to place a reflection plate, a liquid crystal cell, one or more optical compensation sheets, and a polarizing plate in the order of mention.
Since LCD is not a light emitting type display device, it needs an area light source. As one mode of the area light source, a backlight type having, between a liquid crystal cell and an emission light source, a member having a light diffusion capacity such as diffusion sheet or prism sheet to provide a uniform area light source has been used widely and a cold cathode fluorescent lamp (CCFL) or LED is used as an emission light source thereof. Some LCDs are known to use, as an area light source thereof, a combination of a light source placed at an edge portion of a light guiding plate and a diffusion sheet or prism sheet. In these devices, in general, a linear light source or spot light source is converted into an area light source so that the area light source is made uniform by using a diffusion sheet or diffusion film (light diffusion sheet or light diffusion film).
Among members of the backlight for obtaining an area light source, a diffusion sheet is ordinarily placed between the backlight and a polarizing plate on the side thereof. By placing the diffusion sheet, it is possible to reduce uneven luminance due to a light source and achieve uniform display properties on the screen (JP-A-2000-75134) and at the same time, suppress generation of interference fringes such as moiré due to interference of an incident light with pixels in liquid crystal cells.
In recent years, however, there has been an attempt of reducing the number of members of the liquid crystal display cell or decreasing the number of fluorescent lamps utilized as a light source for lower power consumption. With a decrease in the thickness of an LCD, a distance between the light source of the backlight and the diffusion sheet narrows and therefore it becomes difficult to achieve uniform light diffusion by using a conventional diffusion film. In order to increase this distance as much as possible, the diffusion sheet having a diffusion property on the surface of the polarizing plate on the side of the backlight has been employed as a substitute.
For example, JP-A-2000-75134 proposes a light diffusion polarizing plate containing, in dispersed form, porous amorphous particles and spherical particles and having a light diffusion layer with predetermined properties and use of it enables to omit a light diffusion sheet. JP-A-2001-172403 and JP-A-2003-25504 propose a production process of a light diffusion film having a step of casting a dope containing fine particles onto a support. It discloses that this process enables preparation of a light diffusion film excellent in optical anisotropy and the like.